Motor control system



Oct. 22, 935.

Switch.

WIT ESSES:

I I r C. E. L. DAPPRICH MOTOR CONTROL SYSTEM Filed Feb. 23, 1933 2Sheets-Sheet 1 Oct. 22, 1935. c, E. L. DAPPRICH MOTOR CONTROL SYSTEMFiled Feb. 23, 1933 2 Sheets-Sheet 2 WITNESSES:

INVENTOR CarZ E Dappric/z.

' AT'ToRNEY I Patented Oct. 22, 1935 UNITED STATES MOTOR CONTROL SYSTEMCarl E. L. Dapprich, Edgewood, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application February 23, 1933, Serial No. 658,039

10 Claims. (Cl. 172-274) My invention relates to means for controllingthe operation of a plurality of wound rotor inductor motors.

Numerous applications arise in industry where 5 a group of alternatingcurrent motors are required to operate at substantially identicalspeeds, that is, not necessarily at synchronous speed with reference tothe alternating current supply for the motors, but at some lower speed.

10 Heretofore in the art synchronous motors have been utilized for suchindustrial demands. However, synchronous motor installations areexpensive and must necessarily operate at synchronous speed, and,further, are not well adapted to speed 15 variations which are to be thesame for a plurality of motors.

One object of my invention is to provide for maintaining a plurality ofwound rotor induction motors substantially in synchronism with 20 eachother.

A further object of my invention is to provide interconnections betweencorresponding windings of a plurality of motors to be kept insynchronism with each other, whereby the motors 5 automatically holdthemselves at a common speed for the entire number.

A still further object of my invention is to provide corrective windingsections in induction motors, which have small mutual induction with theworking winding and a high self-induction,

by positioning the corrective sections of the windings of the respectivemotors in the lower portion of the slot and separated from the workingwinding by magnetic bridges.

Other objects and advantages will become apparent from a study of thefollowing specification, when taken in conjunction with the accompanyingdrawings, in which:

Figure 1 shows three wound rotor induction 4,0 motors provided with myinvention;

Fig. 2 shows a similar arangement as is shown in Fig. 1, except that thesecondary windings of the induction motors are disposed in thestationary members of the motors; and

45 Fig. 3 shows a cross-section of the portion of the motor providedwith the working winding and the speed corrective winding.

Figs. 4, 5 and 6 are diagrammatic showings of still furthermodifications of my invention.

50' Referring more particularly to Fig. l of the drawings, Startingswitch designates the conventional motor starter, including thenecessary circuit breakers, whereas buses l, 2 and 3 designate the leadsfor supplying electrical energy to 55 the stators 4, 9 and M of thewound rotor induction motors 5, I0 and [5. Although these motors areshown in the same line, it should be noted that no mechanicalinterconnection is shown, and, in fact, in an actual installation thesemotors may be quite remote from each other hav- 5 ing only theelectrical interconnections hereinafter explained more in detail.

Each of the motors 5, l0 and I5 has rotors 8, l3 and [8, respectively,and these rotors are provided with working windings I, I2 and I1,respec- 10 tively, and speed corrective windings 6, H and 16,respectively, the main or working windings of the respective motorshaving corresponding junctions, or, as in this case, slip rings 3!, 32and 33, 35, 36 and 31, 39, Ml and 4! connected to the respectiveconductors 34, 38 and 42. These lastnamed conductors are merely theleads which interconnect the secondary windings or rotors to the commoncontrol rheostat 43 having the switches 44, 45, 46 and 41 for varyingthe speed and torque of all of the motors simultaneously. It is, ofcourse, understood that a common rheostat is not an essential, but thatindependent rheostats may be utilized for each of the secondary windingsof the motors. However, to facilitate the solving of the problem hereinpresented, it would in such case be desirable to have the independentrheostats mechanically interlocked so that corresponding resistorsections would be short circuited for each motor for a single movementof the rheostat arm.

The speed corrective windings 6, H and [6 of the motors 5, l0 and I5,respectively, have corresponding junctions, or, as in this case, sliprings I9, 20 and'2l, 23, 24 and 25, 21, 28 and 29 connected to commonconductors 22, 26 and 30. Since corresponding slip rings of the rotorsof the induction motors for the corrective windings are connected to thesame conductor, no torque will be produced by the speed correctivewindings when all of the rotors of the induction motors are operating atthe same speed, regardless of the slip there may be with reference tothe frequency of the current supplied to the primary or stator windings4, 9 and M, respectively. However, when any one of the three motors lagsbehind any one of the other motors, circulating currents will beproduced in the speed corrective windings through the common conductors22, 26 and 30, and the torque produced in the motor, which is not at theproper speed, will be in such a direction as to accelerate ordecelerate, as the case may be, that motor to bring it to the speed ofthe remaining motors. It is thus obvious that the speed correctivewindings automatically maintain all 01' the motors at the same speed,even though there may be some difference in the load each motor iscalled upon to operate.

In some applications, it may be found disadvantageous to use thearrangement shown in Fig. 1, which of necessity requires the use of sixslip rings on the rotor or secondary winding of each induction motor.Accordingly, the modification shown in Fig. 2 shows the buses l, 2 and 3connected to the rotor windings through the slip rings 5!, 54 and 51,53, 55 and 59, 52, 56 and 58 of the respective motors 50, I00 and I50.It is thus obvious that only three slip rings are necessary for eachmotor. The secondary windings BI, 62 and 63 are provided with the speedcorrective windings 64, 65 and 66, respectively, and these windings, bysuitable junctions, are connected to the respective conductors 22, 26and 30. The working secondary windings 60, 61 and 68 are connected tothe conductors 3B, 42 and 34 and the rheostat 43.

It is, of course, obvious that where the motors are substantiallyidentical in design, and drive loads which are substantially equal, thecorrective torques need only be small, and in consequence the correctingwinding need be only a small portion or fraction of the winding of theentire secondary for each motor, whereas ii. the loads on the motors areconsiderably different, and particularly where the size of the motorsare not the same, the corrective portion of the winding may be largerelative to the secondary. It will be noted that my invention requiresno additional resistors in the control scheme, and in consequence theefflciency of the system is high.

For the circuit arrangement shown if the ef- Iective resistance in theworking section of the secondary winding is varied, or even shortcircuited, the corrective section is also short circuited. To thus notlose or impair the eilective operation or control action of thecorrective section of the secondary winding, it is desirable to disposethe corrective winding in the lower portion of the slots so that themutual induction of the windings may be a minimum. Further, to decreasethe mutual induction between the windings, a magnetic bridge H coactingwith the laminations 10, may be disposed between the working winding 1and the corrective winding 6, as is shown in Fig. 3. It should be notedthat, by thus positioning the corrective winding 6 in the lower portionof the slot and in addition providing the magnetic bridge H, theself-induction is made high. Both of these conditions, that is, a lowmutual inductance and a high self-inductance, are thus attained by thearrangement shown in Fig. 3, and both of these effects improve thecorrective action of the speed corrective winding 6, even though theeffective resistance in the working winding may be varied over aconsiderable range by the rheostat 43.

It will be noted that in Fig. 4, the armature windings oi the respectivemotors are connected to the buses I, 2 and. 3 in the same manner as isshown in Fig. 2 and insofar as the same elements are utilized, thereference characters are chosen alike. It should, however, be noticedthat the corrective windings and ill in this modification are notelectrically interconnected with the working windings 60 and 61, butrepresent inde pendent windings for each motor; are disposed in thebottom of the slot of the stator, as shown in Fig. 3; and are singlephase windings. Each single phase winding has corresponding Junctions 82and 83, and 84 and 85 connected to the buses IDI and I02, respectively.Since the corrective windings in each machine are connected in series inthe same sense, no circulating current will 6 flow in these correctivewindings when the rotors of the two machines rotate at the same speedwith the reference to the frequency of the current supplied to themachines.

The modification shown in Fig. 5 is in all re- 10 spects similar to themodification shown in Fig. 4, except that for this modification thecorrective winding is again not conductively related to the workingwinding but is connected in Y circuit relation for each machine.Corresponding junc- 15 tions 86 and B1, and 88 and 89, and 90 and Si ofthe Y connected corrective windings are connected to the buses 22, 26and 30.

In the modification shown in Fig. 6, the corrective winding is shownconnected in delta 20 circuit relation and has corresponding junctionsalso connected to the buses 22, 26 and 30.

I am, of course, aware of the fact that my invention, particularly forthose skilled in the art after they have had the benefit of the teach-25 ings of my invention, may be embodied in still differentmodifications but I wish to be limited only by the pertinent prior artand the appended claims and not to the specific arrangements shown anddescribed.

I claim as my invention:

1. In a system of control for a plurality of wound-rotor inductionmotors all supplied with alternating current from the same source of supply, a speed corrective winding for each motor 35 disposed in the bottomof the slots of each motor, magnetic bridges disposed in the slots ofeach motor above the speed corrective windings, working windings in thetop of the slots of each motor, means for varying the effectiveresistances 4 oi the working windings to control the operation oi! themotors, and circuit connections for interconnecting corresponding pointsor the rerespective speed corrective windings.

2. In a system of control for a plurality of woundrotor induction motorsall supplied with alternating current from the same source of supply,each of said motors having a primary winding and a pair of secondarywindings, said secondary windings comprising a working winding 50 and aspeed corrective winding, and means for connecting corresponding pointsof the speed corrective winding of all the motors to common junctions.

3. In a control system for a pair of alternating current inductionmotors of the wound-rotor type, each motor having a pair of secondarywindings disposed in slots, one of said windings being disposed in thebottom of the winding slots and the other of said windings beingdisposed 59 in the top of the winding slots, and means forinterconnecting corresponding points of the winding in the bottom of theslots of the two motors to maintain the speeds of the two motors thesame.

4. A wound-rotor induction motor having a secondary winding, acomparatively large part of the winding being connected to a controlresistor and the remaining relatively small portion being mounted on themotor to be subject 70 to but a small inductive effect from the largepart of the winding and having a large self-inductive effect, incombination with another motor similar in every respect to thefirst-named motor and means for connecting corresponding 75 points 01'the small portions of the windings to common junctions.

5. In a system of control for n wound-rotor induction motors where n isany integer other than one, each motor having a primary winding,connecting circuits for connecting all the primary windings to the samesource of alternating current, each motor having secondary windingscomprising a working winding having speed control means interconnectedtherewith, and a speed corrective winding, said speed corrective windinghaving circuits connecting corresponding points of the speed correctivewinding to common junctions.

6. In a system of control for n wound-rotor induction motors, where n isany integer other than one, each motor having a primary winding,connecting means for connecting the primary windings to the same sourceof alternating current, each motor having a secondary winding includinga speed corrective winding disposed in the bottom of the slots for thesecondary winding, a working winding disposed in the top of the slotsfor the secondary winding, and speed control means for the workingwinding only, and means for connecting corresponding points of the speedcorrective winding to common junctions.

7. In a control system for a pair of alternating-current inductionmotors of the wound rotor type, each having a pair of independentlyconnected secondary windings, one of said windings, for each motor,being disposed in the bottom of the winding slots, and the other beingdisposed in the top of the winding slots, and means for interconnectingcorresponding points of the windings in the bottom of the slots of thetwo motors to maintain the speeds of the two motors the same.

8. In a system of control for a plurality of wound-rotor inductionmotors all supplied with alternating current from the same source 01'supply, each of said motors having a primary winding and twoindependently connected secondary windings, said secondary windings em-5 bodying a working winding and a speed corrective winding,respectively, and means for connecting corresponding points of the speedcorrective winding of all the motors to common junctions. 10

9. In a system of control for n wound-rotor induction motors, where n isany integer other than one, each motor having primary windings,connecting circuits for connecting all the primary windings to the samesource of alternating cur- 15 rent, each motor having a pair ofindependently connected secondary windings comprising working windingsand speed corrective windings, respectively, and means for connectingcorresponding points of the speed corrective windings to 2 commonjunctions.

10. In a system of control for n wound-rotor induction motors, where nis any integer other than one, each motor having a primary winding,

a source or alternating-current energy, connect- 25 ing circuits forconnecting all of said primary windings to said source ofalternating-current energy, each motor having a pair of independentlyconnected secondary windings comprising respectively, working windingsand speed correc- 3 tive windings, said working windings being disposedin the top of the winding slots and said speed corrective windings beingdisposed in the bottom of the winding slots, speed control means for theworking windings, and means for conmeeting corresponding points of thespeed corrective windings to common junctions.

CARL E. L. DAPPRICH.

